1. Field of the Invention
The invention relates to a self-pumping hydropneumatic spring strut with internal leveling, in particular for motor vehicles, with a working cylinder which is filled with damping medium under the pressure of at least one gas cushion arranged in a high-pressure chamber and acting as a spring. The working cylinder is divided into two working spaces by a working piston carried by a hollow piston rod and provided with valves. A piston pump is driven by the spring movements and pumps oil out of a low-pressure chamber into the working space connected to the high-pressure chamber and comprises a pump space formed by the hollow piston rod, a pump rod connected to the working cylinder, and a further pressure generator, which acts upon the damping medium.
2. Description of the Related Art
A prior art self-pumping hydropneumatic spring strut in which a damping medium is pumped into a working cylinder by a piston pump of the spring strut while the vehicle is being driven until the ride height of the vehicle is achieved is already known, for example, from German reference DE 196 35 880 Al. Once the correct ride height has been achieved, the working cylinder opens a bleed opening and, with the aid of a short circuit (bypass), the vehicle body is thus prevented from being raised further. These spring struts furthermore have devices which allow the vehicle body to be raised to its ride height while the vehicle is stationary by virtue of the ability to pressurize the damping medium in the pump space by another drive means. Once the appropriate valves have been opened, this drive element effects a pressure balance between the pump space and the working space connected to the high-pressure space, thus allowing the vehicle body to be raised while stationary without supplying oil, fluid or damping medium from an external reservoir.
Due to the way in which the nonreturn valves are incorporated into the design the pump space can only be acted upon by an external pressure generator from the outer end of the piston rod in such spring struts.
It is the object of the invention to develop a spring strut with internal leveling and a raising system which is effective when the vehicle is stationary in such a way that it is possible to provide a compact unit that is easy to install.
To achieve this object, the invention includes a high-pressure chamber and/or a working space of a working cylinder connected to the high-pressure space to be acted upon directly or indirectly by a pressure generator.
The pressure generator may be flanged to an external casing of the spring strut or the pressure generator may be at least partially integrated into the casing of the spring strut, thereby allowing certain components of the pressure generator to be fitted within the spring strut and other components to be fitted outside the spring strut. It is advantageous here if the pressure generator with its corresponding connections is provided in the vicinity of the high-pressure chamber or the working space connected to the high-pressure chamber.
For satisfactory control of the externally applied pressure by the further pressure generator, a further embodiment includes a first nonreturn valve leading from the pressure generator to the high-pressure chamber.
A further embodiment includes a second nonreturn valve leading from the low-pressure chamber to the pressure generator.
In an arrangement which is simple in terms of production, the pressure generator is arranged at the outer circumference of the working cylinder.
According to a further embodiment, the pressure generator includes a piston acted upon by a motor-driven eccentric. In this embodiment, an electric motor may be provided as the motor drive.
As an alternative, the pressure generator may also comprise a gear pump instead of a motor-driven eccentric and piston.
In yet another embodiment, the pressure generator may comprise an axially moveable piston acted upon by an electromagnet.
To provide an economical solution, a pressure generator according to the present invention may be connected to act on at least two spring struts.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.